Marriott is hardly the only hotel partnering with WN. Gosh, it's not even the only hotel partnering with WN that has a Chase card (they also still partner with Hyatt, though given the stay pattern you just described, and given Hyatt's small count of properties, that's not likely to be a good option for you).

Here's the whole list:

http://www.southwest.com/rapidrewards/partners-hotels

As you can see, it includes several hotel programs with brands that are typically lower-priced than either Hilton or Marriott properties. So if you're a leisure traveler, I'm not sure if it makes sense to focus all your paid stays only on Marriott. BW and/or Choice and/or WyndhamRewards might be a much more economical alternative for earning WN points on cheap hotel stays you pay for. (Thought with those brands, you need to check reviews of particular properties even more than with Hilton or Marriott.)

Remember, nothing says you have to use credit card points on the same hotels you stay at. With the exception of Hilton (and occasional promos at a couple other programs), you can't earn miles (ie, WN points) and hotel points on the same stay. So if you are choosing hotels to earn WN points, you aren't building up points in that hotel program anyway from stays (only from CC).

Meanwhilel, while Chase Sapphire Plus will give you flexibility, it may give you the earning power of, say, a Marriott card or a Hilton card, at certain types of merchants. The Marriott card as well as the (free version of) the Hilton card give you double points on restaurants, and even more than double points on stays.

Furthermore, you can get big bonese each from Chase Sapphire Plus and Marriott Rewards Premier, while you'll only get half the bonusese if you only get one of those cards. So for at least a year, I'd recommend you have both. Then see which ones it make sense to keep once the annual fees come up. As I've mentioned, the Marriott card will give you a free night certificate every year that you have to pay the annual fee, so if you can use that cert and get at least as much value from it as the $85 annual fee, why not keep the card, if you're after Marriott points? Then only use it where you get double points, and use the Chase Sapphire Plus elsewhere.

Similarly, for WN, you can get tons of free flights if you sign up for the right WN card at the right time. Keep it for a year, and then when the next annual fee comes up, if it doesn't seem worth keeping, then close it. But again, you'll earn an extra bonus by also getting a WN card, that you can't get from just getting one Chase Sapphire Plus card. And unless you have very high spend, say from a business, it'll take a long time for you get as many points from spend on the Sapphire card as you'll get from sign-up bonuses on the WN cards and the Marriott cards.

Naturally, since these are all Chase cards, you probably don't want to apply for all of them at the same time. But spacing the apps a few months apart, it shouldn't a problem to get all 3.